1. Field of the Invention
The present invention relates to a secondary battery. More specifically, the present invention relates to a pouch-type lithium secondary battery with easy adjustability of an electrode tab position.
2. Description of the Related Art
With continuing recent trends towards weight reduction and higher functionalization of a variety of products including electric tools and portable wireless devices such as video cameras, cellular phones, notebook computers, and personal digital assistants (PDAs), there is increasing importance of the batteries used as a power source for these products. This interest has been matched by a great deal of research and study of these batteries.
Particularly, intensive interest has been given to rechargeable lithium secondary batteries which advantageously exhibit rapid chargeability and high energy density per unit weight due to the light nature of lithium atoms, as compared to conventional lead storage batteries, nickel-cadmium (NiCd) batteries, nickel-hydrogen batteries, nickel-zinc batteries, and the like.
Typically, lithium secondary batteries use a non-aqueous electrolyte due to potential reactivity of lithium with moisture. Such an electrolyte may include a lithium salt-containing solid polymer or a liquid electrolyte containing a lithium salt that is dissociated in an organic solvent. Generally, the organic solvent in which a lithium salt is dissolved may be ethylene carbonate, propylene carbonate, other alkyl group-containing carbonates, and the like. These solvents have boiling points of 50° C. or higher and very low vapor pressure at room temperature.
Lithium secondary batteries may be categorized into two groups including lithium metal batteries and lithium ion batteries that use liquid electrolytes and lithium ion polymer batteries that use solid polymer electrolytes.
The lithium ion polymer battery may employ a multilayer pouch composed of a metal foil layer and one or more polymer layers covering the metal foil, instead of a metal can of the lithium ion battery. Use of the multilayer pouch can advantageously result in significant weight reduction of a battery, as compared to use of the metal can. Usually, aluminum is used as a metal constituting a foil in the multilayer pouch. Further, a polymer layer forming an inner layer of the pouch film protects the metal foil against attack of an electrolyte and simultaneously inhibits possible short-circuits between positive and negative electrodes and/or between electrode tabs. The lithium secondary batteries using such a multilayer pouch are conventionally referred to as pouch-type lithium secondary batteries.
For fabrication of the pouch-type lithium secondary battery, a positive electrode, a separator and a negative electrode are first stacked, or stacked and wound to form an electrode assembly which is then placed in a pouch. Subsequently, an upper pouch film and a lower pouch film are thermally fused to each other in open edge portions of the pouch to form a bare cell battery of a sealed pouch type.
Accessories or structures such as a protection circuit module (PCM) or a positive temperature coefficient (PTC) device are attached to the bare cell battery to form a core pack battery.
By coupling the resulting core pack battery within a hard case, a complete hard pack battery is produced.
Conventionally, a pouch-type lithium secondary battery is of a generally square or rectangular pouch shape, and first and second electrode tabs connected to an electrode assembly are drawn outward from the pouch. Here, the first and second electrode tabs are always disposed at a certain distance from each other and attached to the electrode assembly.
However, a battery pack recently fabricated by the pouch-type lithium secondary battery should be designed with a different spacing between the first electrode tab and the second electrode tab, depending on the kinds of electronic devices.
To this end, relevant modifications of battery manufacturing processes should be made depending on design conditions of battery packs to which the batteries are applied upon fabrication of the pouch-type lithium secondary batteries.